1. Field of the Invention
This invention relates to a process for recovering bitumen from tar sand and, more particularly, to a combination hot-water and thermal process utilizing a fluidized bed to separate products and to produce a coked sand, a portion of which may be recycled into the hot-water process as well as through the fluidized bed.
2. The Prior Art
The term "tar sand" refers to a consolidated mixture of bitumen (tar) and sand. Alternate names for tar sands are "oil sands" and "bituminous sands", the latter term being more technically correct in that the sense of the term provides an adequate description of the mixture. The sand constituent of tar sand is mostly alpha quartz, as determined from x-ray diffraction patterns, while the bitumen or tar constituent of the tar sands consists of a mixture of a variety of hydrocarbons and heterocyclic compounds. This bitumen, if properly separated from the sands, may be upgraded to a synthetic crude oil suitable for use as a feedstock for the production of liquid motor fuels, heating oil, and/or petrochemicals.
About 65 percent of all of the known oil in the world is contained in tar sand deposits or heavy oil deposits. Tar sand fields occur throughout the world with the exception of the continents of Australia and Antartica. Significantly large tar sand deposits have been identified and mapped in Canada, Columbia, Trinidad-Tobago, Venezuela, and the United States. The Canadian tar sand deposits, known as the Athabasca tar sands, are located in the province of Alberta, Canada and are currently being developed. The estimated reserves for the bitumen content in the Athabasca tar sands alone has been estimated to be approximately 900 billion barrels. In the United States, approximately 24 states contain known tar sand deposits, although about 90 to 95 percent of the mapped tar sand deposits are located within the State of Utah and are estimated to include at least 25 billion barrels of oil. While the Utah tar sand reserves appear small in comparison with the enormous potential of the Athabasca tar sands, the Utah tar sand reserves represent a significant energy resource when compared to the United States crude oil proven reserves (approximately 31.3 billion barrels) and with the United States crude oil production of almost 3.0 billion barrels during 1976.
Utah tar sand deposits occur in six major locations along the eastern edge of the State with the bitumen content varying from deposit to deposit as well as within a given deposit. Current information available indicates that Utah tar sand deposits average generally less than 10 percent bitumen (by weight), although deposits have been found with a bitumen saturation of up to about 17 percent (by weight). Unlike Athabasca tar sands, however, Utah tar sands are characterized by the absence of connate water. In the absence of connate water, it is obvious that the bitumen is directly in contact with and bonded to the surface of the sand grains. Tests have also determined that the bitumen of Utah tar sands is at least one order of magnitude or at least ten times more viscous than bitumen obtained from Athabasca tar sands. Accordingly, the processing of Utah tar sands involves both displacement of the bonded bitumen from the sand grains followed by subsequent phase disengagement of the more viscous bitumen from the residual sand phase. Attempts to use conventional hot water processes that have been successfully applied to the Athabasca tar sands have been unsuccessful for processing Utah tar sands. This failure is readily apparent in light of the recognized differences in both the physical and chemical nature of the Utah tar sands.
A more comprehensive discussion of the Athabasca tar sands may be found in the literature including, for example, (1) E. D. Innes and J. V. D. Tear, "Canada's First Commercial Tar Sand Development," Proceedings of the Seventh World Petroleum Congress, Elsevier Publishing Co., 3, p. 633, (1967); (2) F. W. Camp, The Tar Sands of Alberta Canada, 2nd Edition, Cameron Engineering, Inc., Denver, Colo. (1974); and (3) J. Leja and C. W. Bowman, "Application of Thermodynamics to the Athabasca Tar Sands," Canadian Journal of Chemical Engineering, 46 p. 479 (1968).
Additionally, the following U.S. Patents are a few of the patents which have been granted for apparatus or processes directed toward obtaining bitumen from tar sands: U.S. Pat. Nos. 1,497,607; 1,514,113; 1,820,917; 2,871,180; 2,903,407; 2,927,007; 2,965,557; 3,159,562; 3,161,581; 3,392,105; 3,401,110; 3,553,099; 3,560,371; 3,556,980; 3,605,975; 3,784,464; 3,847,789; 3,875,046; 3,893,907; and 4,120,776. With the exception of U.S. Pat. Nos. 3,605,975 and 4,120,776, a coinventor of which is also a coinventor herein, each of the foregoing patents have been directed toward processing Athabasca tar sands and, as indicated hereinbefore, are believed not directly applicable to processing Utah tar sands.
The latter patent, U.S. Pat. No. 4,120,776, discloses a hot-water/caustic process for recovering bitumen from Utah tar sands. Greater than 95 percent of the bitumen was recovered in a concentrate which typically analyzed on the order of about 65 percent bitumen for single-stage processing. The sand tails were relatively free of bitumen. Accordingly, as set forth in this patent, the recovered, high-bitumen content concentrate would require additional upgrading before it can be successfully used in a refining process. It would, therefore, be a significant advancement in the art to incorporate the foregoing process in a process which upgrades the bitumen-rich concentrate to readily adapt the same for further processing and/or transfer by pipeline. It would also be an advancement in the art to provide a novel thermal process wherein a portion of the coked sand is recycled into the hot-water system to provide improvements in phase disengagement of the bitumen and also to transfer thermal energy to the hot-water system. Such a novel process is disclosed and claimed herein.